Coupling device for micro-wave energy



June 19, 1951 V E. c. oKREss 2,557,391

i COUPLING DEVICE FO MICROWAVE ENERGY Filed Oct. 7, 1942 y 3Sheets-Sheet 1 INVENTOR E C` O/f/FSS ATTORNEY June 19, 1951 E. c. oKREssCOUPLING DEVICE FOR MCROWAVE ENERGY s sheets-sheet 2 Filed Oct. '7. 1942Rx. w m.

June 19, 1951 E. c. oKREss COUPLING DEVICE FOR MICROWAVE ENERGY K FiledOct. 7, 1942 3 Sheets-Sheet 5 INVENTOR E'. C. OAT/:'55s

ATTORNEY Patented `lune 19, 1951 UNlTED STATES PATENT OFFICE ooUPLINGDEVICE Fon MICRO-WAVE ENERGY f l v Ernest Carl Okress, Montclair, N. J.,assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa'., acorporation of Pennsylvania Application October 7, 1942, Serial No.461,135

8 Claims. (C1. 178--44) This invention relates to coupling devices andmore particularly to a coupling device for microwave energy, as forinstance, from the source of generation of the energy to a wave guide orother means of transmission of the energy from such source to effectuateits use.

While coupling devices per se are known in the art, difficulties havebeen experienced in connection therewith both as to the efficiency, asto the tuning ,and as to the mechanical assembly. In this latter respectit has been found diflicult .to construct a frictional coupling devicewith such accuracy that the metallicparts will not either in assembly orin use introduce strains upon the glass envelope portion and immediatelyo r ultimately cause a crack or other rupture therein which renders thedevice inoperative or grossly ineicient as to require discarding theentire coupling device.

It will be recognized by those skilled in the art .that a couplingdevice is in effect a `short length of coaxial line with a loop o rother terminal for introduction into the generator and thatAconsequently, since the generator is evacuated and the wave guide withwhich the device is coupled is not evacuated, a .dielectric has to beinterposed in the energy path for maintaining the evacuation of thegenerator. Various schemes have been suggested and tried, and it appearsmost `effective to extend rthe coaxial pick-up rod portion of theterminal from the generator Y to the wave guide with said `rod `portionpassing transversely through the wave guide .and intersecting the centerline of the wave guide at right angles, the portion of the rod Withinthe wave guide constituting what may b e appropriately termed anantenna. To accomplish this desider- `atumy a dielectric envelope, ofglass, :issealed at one end to the tubular portion of the coaxial lineand is sealed at its other end toa distant part of the rod portion ofthe coaxial line, said dielectric envelope extending with the rodthrough the wave guide and the two areas of sealing above mentionedbeing at oppositeexterior portions of the wave guide. This .constructionnecessitates that there shall be not only this inechanical attachment totheparts mentioned but, of necessity, means to establish the required.antenna reactance and radiation resistance in order that the waveguidemaybe matched to an input having an impedance less than twicetheAappropriate characteristic Wave guide impedance.

An object .of the invention is to overcome the aforementioneddifliculties and to improve the coupling device both mechanically and'froman leiiiciency standpoint.

'adjustments for the reflecting and tuning means which is entirelyoutside of t he evacuated area and in operation introduces no movementof the envelope for the evacuated area or of any parts extending,thereinto Y vStill further objects of the invention are sirnplieitv .ofparte, ease and permanence 0i' assembly, and adaptability Ato knowngenerators and wave guides.

Additional objects of the invention will appear'to -those skilled in theart both by direct reference thereto as the description proceeds .and byimplication from .the context.

Referring to the accompanying drawings in which like numerals ofreference indicate similar parts throughout the several views,

Figure 1 isa sectional view longitudinally of my improved couplingdevice and of a Wave guide with which it is associated;

Figures 2 and 3 are cross sections on lines I-II and III-1.11.1,IBSpeCiiVelY, .Of Figure il;

Figures 4, 5 and 6 are sectional views of the character o f Figure 1,but left partly in elevation, and .each .showing a meded construction;

illustrated in said drawing and referring initially to the constructionof YFigures 1, .2 and .3; the reference numeral Ill designates a part ofa known ultra-high frequency generator from which waveenergy isderivable through la coaxial line means which includes a current Iprobeor loop vIl ofsuitable shape situated within a cavity I2 of thegenerator. The interior of said generator, including said cavity, isevacuated and .it isJ of Course, essential .to maintain the vacuum.throughout the useful life of said generator.

Normally the current probe orjloop Il is exposed direetlyte theevaeuatedcavity.

The desigieratum istotransfer energy` picked .up by the probe .erleep te.a'hollow waveguide L3 Situated .exterior te the generator `and thehollow of which is not evacuated. Wave guides in `general are known to.the art and constitute e means .by ,Whieh .electromagnetic energy' isprepagatedr from one .place .te .another .befereits ultimatetransmission in free space or utilization in some other instrumentality.Usually wave guides are rectangular in cross section with one dimensiongreater than the other for purposes of obtaining the desired mode ofoscillation and polarization of the wave that may be transmitted. Thecross-sectional dimensions have a definite relation to the character ofthe wave being transmitted, but need not be discussed in thisspecication. Suffice it to say, that the terminal sections heredisclosed are suitable for launching the transverse electric, TEoi, modeor Hoi wave. For a more extended discussion of modes and waves involvedreference may be made to an article by L. J. Chu and W. L. Barrow,entitled Electromagnetic waves in hollow metal tubes of rectangularcross section published in Proceedings of Institute of Radio Engineers,vol. 26, No. l2, December 1938, beginning page 1520, and of especialinterest, page 1532.

The coupling device per se comprises, in addition to current probe orloop I I above mentioned, a coaxial line of which the center rod I4 isthe axial portion and is a continuation of the said current probe, thatportion of said rod which is within the wave guide being termed theantenna, and that part from the generator to the wave guide being termedthe pick-up portion. The rod is of tungsten, copper and/or othersuitable metal and projects from the generator to and vertically throughthe wave guide medially between the side walls thereof therebyintersecting the center line of said wave guide. The cooperating tubularportion of the coaxial guide is constituted by a conductive base ormounting thimble I5, as of copper, and by a tube I5 which preferably isalso copper, axially alined and projecting upwardly therefrom, both thethimble and the tube having central passages I1, I8, respectively, ofwhich one is a continuation of the other. The upper end of said tube I6is substantially at the level of the lower horizontal wall of the waveguide but does not have any contact therewith.

Also projecting from the upper end of said thimble, preferably coaxialwith the said tube I6,

but of less length than said tube is a sleeve I9 the upper end of whichis sealed vacuum tight to an end margin of a long glass envelope ofsubstantially the same diameter throughout its length as said sleeve.The sleeve and glass envelope are of materials having substantially thesame co-eicient of expansion and by preference f the glass isborosilicate glass and the sleeve is an alloy of nickel, cobalt,manganese and iron in accordance with disclosure of Patent 2,062,335 orDecember 1, 1936 to Howard Scott, said material being sold under thetrade name of Kovan Glass envelope 20 extends upwardly through the waveguide and is sealed, as with reentrant stem 22 to the central rod I4 ata position on said rod above the wave guide, said rod in this instanceextending through the seal and projecting from the upper end of theenvelope. Standing upright above the wave guide to which it is attached,is a. sleeve-like metallic housing 23 coaxial with the said rod andenvelope. The envelope and rod both project into said housing.

Located within said housing above the envelope and around the projectingend of rod I 4 is an annular hollow piston 24 having an outercylindrical skirt portion 25 and an inner cylindrical skirt portion 26connected at their upper ends by an annular end wall 2'I. This piston 24accordingly provides a central bore or passage 28 axially therethroughand provides between said cylindrical skirts 25 and 2B an annulardownwardly opening chamber 29 the depth of which from open end 30 to endwall 2'I is a coaxial quarter wave length in the dielectric present,which in this instance is air. It is appropriate to point out thatcentral bore 28 is considerably larger than the diameter of the rodaffording ample clearance to avoid contact therewith notwithstandingimperfections of manufacture, misalinement from assembly or distortionsin use. Furthermore, a similar clearance or gap 3I is provided betweenthe outside cylindrical skirt 25 and the housing 23 containing the same.These clearances are necessary in view of the fact that in operationvery high currents seek to traverse the space between the rod I4 andhousing 23 and a sliding contact connecting those parts is generallyelectrically undesirable and mechanically detrimental. The chamber 29 ofthe piston is a coaxial quarter-wave length deep, with a high impedanceat the open end 36, which acts as a mirror or perfect open coaxial line.

Support and adjustment for the piston 24 is obtained by a screw 32,threaded through the end of the housing 23 and shown with a knurled head33 at its outer end for manipulation by hand. A lock nut 34 on the screwcan be tightened against the housing and retain the screw in itsadjusted position. The inner end of the screw is provided with a flare35 of inverted cup-like shape with the lower rim thereof secured to theend wall 24 of the piston. The flare 35 is of adequate depth toaccommodate the upper end of the rod I4 projecting thereinto. The properantenna reactance can be obtained by adjusting the position of thepiston 24 in the tube or housing 23.

The introduction of the proper radiation resistance for the antenna isaccomplished by provision of an appropriate closure for one end of thesaid wave guide. Preferably said closure comprises a piston 38rectangular in cross section to correspond to the shape of the waveguide and having a skirt portion 38 forming an interior chamber 39 whichis a quarter wave length deep and opens toward the coupling device. Thispiston provides an end wall 40 from which said skirt 38 projects. On theother side of the end wall 40 from the said skirt is a reduced portionor neck 4I which connects with a rectangular head portion 42 ofappropriate size to have sliding t with the interior face of the waveguide. It will be noted from the drawing that the skirt portion 38 is ofless dimension than the inside dimension of the wave guide so as toprovide a gap 43 between said skirt portion and the wave guide. Thereexists a high impedance at the forward open end 6I since the pistonchamber is a quarter wave-length deep, referred to wave guide wavelength. In order to adjust this piston for altering the radiationresistance of the antenna the head 42 thereon is connected to a screw 44rotatyA fixed closure 4'I is screwed to the end of the wave guide as bybeing attached to a collar 48 which partly engirdles the end margin ofthe wave guide and retained thereon by suitable means, such as screws49. Adjusting screw 44 has a suitable finger piece such as the knurledknob 50 and is retained in adjusted position by a lock nut 5I adapted tobe turned tightly against the end of xed housing 41.

Electrical continuity between the upper end lsaid rings, envelope sleevei6.

of coaxial tube I and the adjacent wave guide bottom wall is obtained bymeans set forth in and `forming the subject matter of co-pending appli--opposed on the outside of the envelope by a metallic ring 53 the upperend of which connects with the wave guide. Surrounding the metallic ring53 is a glass ring 54 having the same dielectric constant as the glassof the envelope. This glass ring is interposed between the metallic ringand a lower housing 55 which extends from thimble l5 to the wave guideand is concentric with The glass ring, metallic ring and enlargement 52are of a length substantially equal to a quarter coaxial wave length inthe dielectric represented by the glass.

It may now be pointed out that an essential feature of the presentinvention resides in the v provision of a piston of quarter wave lengthdepth out of contact from the surrounding wall of the structure in whichit is used. While Figure 1 illustrates use of two such pistons both ofwhich are adjustable at any time, it is equally within the scope of theinvention to provide a piston which can be adjusted at the source ofmanufacture and permanently soldered in place after the adjustment hasbeen made. A modification illustrative of this permanently adjustedstructure is shown in Figure 4. Referring to this View in detail,envelope 25 with its contained coaxial rod Ma together with supportingthimble l5 and lower housing 55 conforms to the construction al readydescribed. Upper housing 23a differs from the preceding construction inthat it is open at its upper end. A piston 2da is situated in thehousing 23a said piston having outer and inner cylindrical skirts 25aand 25a with an upper end wall 21a. As before, a central bore or passage28a. is provided through the cylindrical inner skirt leaving ampleclearance for the rod ille.

Between the said inner and outer skirts 25a and 26a an annulardownwardly opening chamber 25a depth of which from open end 35a to endwall 21a is a quarter coaxial wave length in air. At the upper side ofend wall 2id is a reduced portion or neck '56 which connects thereabovewith a head 5l the size and shape of which is such that it ts within theopen upper end of housing 23a. After adjustment has been made this headis soldered, as at 553, to the housing and retains that adjustedposition thereafter. It is to be noted that although head 5l nts thehousing there is a gap Sla separating the outer skirt 25a from contactwith said housing.

Piston for radiation resistance yadjustment is provided, and adjustmentaccomplished in a manner similar to the construction heretoforedescribed. In this instance, piston 35a is rectangular and provides askirt portion 38a forming a chamber 39a therein with a depth to the endwall 45a equal to a quarter wave length in air, referred to wave guidewave length. At the outer side of said end wall lila is a reducedportion or neck 41a and therebeyond a head 42a. The headis ofappropriate dimension and has a sliding t with the wave guide whereasthe skirt portion 38a is of a smaller dimension so as to leave aclearance or gap 43a 'between the skirt and the wave guide. After thepiston is located at the desired adjusted position at the place ofmanufacture it is permanently secured las by solder 59.

While the foregoing construction has many advantages outstanding amongstwhich is the fact that the open front edge of the piston constitutes ahigh impedance and, therefore, makes it immaterial as to the structureo1' impedance at the rear of the piston, certain advantages are to begained by reversing the piston and having the solid wall toward thefront and the open end projecting vrearward with modifications in thedepth of cups however. Essential among these differences is the factthat the latter construction permits closer association of the piston tothe center line of the wave guide in the instance of the piston on theaxis of the probe or closer to the center line of the probe in theinstance of the piston at the end of the wave guide. Also the coaxialquarter wave length rather than the wave guide wave length is used indetermining the depth of the inverted rectangular cup 36h. Reversing thepiston has the effect of a movable shorted line instead of a movableopen line as in Figure l. A construction including pistons Zlib and hhaving the solid faces 2lb and 40h thereof forward is illustrated inFigure 5. Care is taken in this construction of Figure 5 to maintainhigh impedance at the planes 35h and Sib of the open rear ends of therespective pistons and low impedance at the forward closed ends thereof.Parts in Figure 5 are designated by the same reference numerals as usedin connection with the description of Figure l, but with the addition ofthe letter b thereafter, so that repetition of description is notbelieved necessary here. It is to be here noted that pistons 26th and350 are a coaxial quarter wave length deep.

lIn connection with the construction shown in Figure 5 the flare 35h forreversed piston 24h extends into the chamber 25h of the piston to themiddle part of end wall 2lb to which it is secured. Likewise withrespect to the other piston 3th, neck Mb extends axially within thechamber 39h of piston 35i) to the forward end wall 4Gb thereof to whichit is likewise attached. As in the preceding construction of Figure l,the piston in each instance is separated from the part of the devicesurrounding the same. In this instance the high impedance is at the gapat the rear open end of the piston whereas the low impedance is at theforward closed end of the piston.

In Figures 6 to 8 an ultra-high frequency generator lc is indicated withprobe Hc entering cavity I2C and projecting therefrom transverselythrough a wave guide H30 by virtue of rod or v antenna formed as acontinuation of said antenna. Thimble having tube Hic next its innerbore, Kovar sleeve and tubular boro-.- silicate glass envelope 2Go areprovided as before, together with enlargement 52C on the tube |50 withinthe envelope and metallic and glass rings 53e and 511C opposed theretoon the outside of the envelope for constituting an impedance section andelectrical continuity at the longer dimension bottom wall of the waveguide. In this showing an impedance section is provided in the upperhousing above the wave guide.

Describing this upper impedance section more in detail, the samecomprises a metallic enlargement S2 of the coaxial quarter wave lengthin glass.` This lenlargement ts upon the rod Mc and is silver soldered,as at 63. The outer peripheral surface of this enlargement is next theglass envelope. Outside the envelope, of same length as and directlyopposed to the said enlargement is a metallic ring 64 and next theretois a glass ring 65 both of substantially coaxial vquarter wave length inglass. The glass ring ts within an upper housing 66 shown as made in twosections for enabling assembly to be accomplished more readily. Theposition of this electrically shorted line is readily obtained once thecharacteristics of the particular type of generator is established. Thissection obtains effect of an electrical shorting and no high frequencypasses therebeyond. This completely avoids heretofore troublesome arcingand corona occurring at the outer end of rod or antenna |40 between saidantenna and housing.

At the end of the wave guide, is provided a reversed piston 36e havingskirt 38e providing a chamber 39e to a forward end wall 40e such thatthe chamber is a quarter wave length deep in air referred to free spacewave length. The piston is supported by a head 42e which fits the waveguide, a neck portion Mc extending from said head into the pistonchamber and connected to the mid part of the forward end wall 40o. As inpreviously described constructions, the skirt 38c of the piston isspaced from the several walls of the wave guide leaving a gap 43etherebetween. The adjustment of the proper radiation resistance isachieved by the movement of piston 36e and when accomplished said pistonis soldered, as at 59o in place.

The reversed piston tuning means above described may be used with otherconstructions of coupling devices, such as the rugged commercialstructure shown in Figure 9. The piston structure is identical in Figure9 with that in Figure 6, wherefore description is not repeated and partsmay be identified by the same numerals but with substitution of letter dafter each. Similarly the upper impedance section of Figure 9 is alsolike that of Figure 6 and a corresponding use of numerals is made.

In Figure 9, ruggedness of structure is obtained by utilizing aninverted cup 61 of Kovar at the top of the glass portion of the enveloped is sealed at its rim to the glass. Rod Idd is secured to the end wallof this inverted cup at the inside thereof. By virtue of the impedancesection in front of the Kovar cup, little energy escapes thereto.'Maximum rigidity and maintenance of accurate spacing of parts isobtained by use of the said inverted cup and by securing the rodthereto.

Referring to Figures 1 and 4, the forwardly facing open ended pistons 36and 36a represent open lines, and the forward plane at 6l and Ela ofeach is substantially a half wavelength distant from the respective rodor antenna I4 and Ma. Similarly, in the same figures, with regard to thecoaxial line pistons 24 and 24a, the forward open end of each is aquarter wave length distant from the center line of the respective waveguide i3 or i3d. With the reversed or inverted skirt pistons of Figures5 to 9, showing the shorted line assembly, the forward plane of thepiston in each case is the solid wall 4Gb, 45e and 40d, and this is at adistance of a quarter wave length distant from the rod or antenna |417,Mc or 14d. With the coaxial construction, the forward plane of thepiston represented by solid wall 2lb, Figure 5, and the forward end ofthe corresponding impedance sections in the upper housings,

are substantially a half wave length from the centerline of therespective wave guide |31), l3c and I3d. Exact location of the forwardplanes of the several pistons is then made so as to produce theparticular antenna radiation resistance and antenna reactance requiredat the point of termination and so are not strictly multiplesof quarterwave lengths.

Since the various details of construction, as well as the preciserelation and functioning of parts, are subject to variation and changeWithout departing from the inventive concept or scope of the invention,it is intended that all matter contained in the specification orillustrated in the drawing, shall be interpreted as exemplary and not ina limiting sense. It is also to be understood that the following claimsare intended to cover all of the generic and specific features of theinvention herein shown and described and all statements of the scope ofthe invention herein set forth as a matter of language which might besaid to fall therebetween.

I claim:

1. A coupling device from an ultra high frequency generator to a waveguide, comprising an elongated sealed and evacuated envelope, a rod ofwhich a part constitutes a pick-up portion and a part constitutes anantenna, both of said parts of the rod being within the vacuum of theenvelope, said rod extending longitudinally of said envelope, saidenvelope and rod being transverse to and projecting through said waveguide and the wave guide having one portion for conveying energy fromthe region surrounding the antenna and having a directly oppositeenclosure portion terminating outwardly from the antenna of the order ofan odd quarter wave length therefrom, vand a closure for the secondmentioned portion, said closure having as part thereof a piston-likemember having a closed end and an open end and forming with theenclosure portion a resonant system by which high impedance isestablished at the open end and low impedance at the closed end of thesaid member.

2. A coupling device from an ultra high frequency generator to a waveguide, comprising an elongated Sealed and evacuated envelope, a rod ofwhich a part constitutes a pick-up portion and a part constitutes anantenna, both of said parts of the rod being within the vacuum of theenvelope, said rod extending longitudinally of said envelope, saidenvelope and rod being transverse to and projecting through said waveguide and the wave guide having one portion for conveying energy fromthe region surrounding the antenna and having a directly oppositeenclosure portion terminating outwardly from the antenna of the order ofan odd quarter wave length therefrom, and a closure for the secondmentioned portion, said closure having a piston as part thereof saidpiston having its cross-sectional dimensions less than the correspondingdimensions of the wave guide thereby forming a gap between the pistonand Wave guide, and said piston having an open to and projecting throughsaid wave guide and the wave guide having one portion for conveyingenergy from the region surrounding the antenna and having a directlyopposite enclosure portion terminating outwardly from the antenna of theorder of an odd quarter wave length therefrom, and a closure for thesecond mentioned portion, said closure having a piston as part thereofsaid piston having a skirt portion therearound open at one end andclosed at the other and of smaller outside dimensions than the insidedimensions of the wave guide, thereby forming a peripheral gap betweensaid skirt and Wave guide, and said skirt providing an open quarterwave-length cavity therein by which impedance is minimized at saidclosedend across the gap.

4. A coupling device from a source of resonant frequency to a Waveguide, comprising a wave guide and an elongated envelope projectingtherethrough, an antenna extending longitudinally of said envelopeconnected to the source of resonant frequency and having an extensionprojecting through the end of the envelope, a metallic housing over saidextension of the antenna and end of said envelope thereat coaxial withsaid antenna and joined to said Wave guide, and a piston in said housingoutside of said envelope and around said extension and out of contactfrom said housing and electrically coupled with low impedance to saidhousing for current flow, said antenna being substantially apredetermined distance from said wave guide the value of whichestablishes the required antenna reactance, whereby the same resonantfrequency existing in the envelope is transferred to the wave guide.

5. A coupling device from a source of resonant frequency to a Waveguide, comprising a wave guide and an elongated envelope projectingtherethrough, an antenna extending longitudinally of said envelopeconnected to the source of resonant frequency and having an extensionprojecting through the end of the envelope, a metallic housing over saidextension of the antenna and end of said envelope thereat coaxial withsaid antenna and joined to said wave guide, a piston in said housingoutside of said envelope for providing impedance matching between saidsource and wave guide, said piston being out of contact'from both saidhousing and said antenna extension, and means productive of lowimpedance by Way of said piston from said antenna extension to saidmetallic housing for providing current flow from said antenna extensionto the wave guide, whereby the same resonant frequency existing in theenvelope is transferred to the wave guide.

6. A coupling device from a source of resonant frequency to a Waveguide, comprising a wave guide, and an elongated envelope projectingtherethrough, an antenna extending longitudinally of said envelopeconnected to the source of resonant frequency and having an extensionprojecting through the end of the envelope, a metallic housing over saidextension of the antenna end of said envelope thereat coaxial with saidantenna and joined to said wave guide, a piston in said housing outsideof said envelope and out of contact from and electrically coupled withlow impedance to both said housing and said antenna substantially at acommon plane transverse to said housing and antenna.

'7. A coupling device from a source of resonant frequency to a waveguide, comprising ua wave guide and an elongated envelope projectingtherethrough, an antenna extending longitudinally of said envelopeconnected to the source of resonant frequency and having an extensionprojecting through the end of the envelope, a metallic housing over saidextension of the antenna and end of said envelope thereat coaxial withsaid antenna and joined to said wave guide, and a piston in said housingoutside of said envelope for providing impedance matching between saidsource and wave guide, said piston having an end wall and a skirt withthe skirt having a longitudinal dimension of an odd quarter wave lengthparalleling said housing and said skirt being out of contact from saidhousing and providing means in conjunction therewith productive of lowimpedance at one end of the piston for current flow from said antennaextension to said housing.

8. A coupling device from a source of resonant frequency to a waveguide, comprising a Wave guide and an elongated envelope projectingtherethrough, an antenna extending longitudinally of said envelopeconnected to the source of resonant frequency and having an extensionprojecting through the end of the envelope, a metallic housing over saidextension of the antenna and end of said envelope thereat coaxial withsaid antenna and joined to said wave guide, and a piston in said housingoutside of said envelope, said piston having an end wall and a skirtwith the skirt having a longitudinal dimension of an odd quarter wavelength and said skirt being out of contact from said housing, said skirthaving its open end toward the wave guide and its end wall at the end ofthe skirt away from the wave guide.

ERNEST CARL OKRESS.

REFERENCES CITED The following references are of record in the le ofthis patent:

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